Cases are usually constructed from steel, aluminum, or plastic, although other materials (such as wood and perspex) have also been used in case designs.

Size and shapeCases can come in many different sizes or form factors. In 2006, the most popular form factor is ATX, although small form factor cases are becoming popular for a variety of different uses.

A case with an ATX motherboard and power supply, for example, may still take on one of several specific shapes, also known as form factors. Common case form factors include towers (such as mini tower, mid-sized tower, and full-sized tower); desktops or pizza boxes (also called flatbed or horizontal); and slim desktops, which integrate the display into the housing. Tower cases are taller and typically have more room while desktop cases are more compact and are more popular in business environments.

Small form factor cases are a variety of cases that are becoming more and more common. Companies like Shuttle Inc. and AOpen have been producing such cases and FlexATX is the most common motherboard designed for them. Apple Computer has its Mac Mini computer, which is around the size of a CD-ROM drive.

Function

A computer case opened up and stripped of its motherboard and power supply unitCases usually come with room for a power supply unit, several expansion slots and expansion bays, wires for powering up a computer and some with built in I/O ports that must be connected to a motherboard.

Motherboards are screwed to the bottom or the side of the case, its I/O ports being exposed on the back of the case. Usually the power supply unit is at the top of the case attached with several screws. The typical case has four 5.25" and three 3.5" expansion bays for devices such as hard drives, floppy disk drives and CD-ROMs. A power button and sometimes a reset button are usually located on the front. LED status lights for power and hard drive activity are often located near the power button and are powered from wires that are connected with the motherboard. Some cases come with status monitoring equipment such as case temperature or processor speed monitors.

A panel on the side, covers up and protects the inside of the computer when being used, which usually slides on and held with a screw. Most cases require a large amount of screws to put together. Recently there has been a move to "screwless" cases, where cases are held together with other methods than screws. Since the early 2000s, some computers have begun to have clear side panels so that the user can look into the computer while it is operating.

Appearance

The current iMac G5 contains the entire computer in a two inch-thick screen—there is no tower.Traditional designs are beige and rectangular, but have evolved in style, especially after the introduction of the iMac in 1998. Beige box designs are typically found on budget machines; some people still prefer the traditional design.

Case modding is the artistic styling of computer encasings, often to draw attention to the use of advanced or unusual components. Modded cases may include internal lighting, custom paint, acrylic windows, or liquid cooling systems. Some case modding hobbyists build their own cases from raw materials like aluminum, steel, acrylic, or wood.

Stickers are common on cases. These may include the manufacturer's logo, the computer's specifications (CPU, RAM, Hard drive, etc), the operating system (such as "Designed for Windows XP") and processor (such as Intel Inside).